Golf Ball Compositions

ABSTRACT

Golf balls consisting of a core and a cover are disclosed. The core is a solid, single-layer core formed from a rubber composition comprising a base rubber, a free radical initiator, and a hydroquinone. A ratio of the amount of the hydroquinone present in the rubber composition, measured in parts by weight, to the amount of free radical initiator present in the rubber composition, measured in parts by weight, is generally from 0.05 to 2. The core has a positive hardness gradient such that the difference between the core&#39;s surface hardness and the core&#39;s center hardness is 25 Shore C units or greater and/or the core has a diameter of from 1.51 inches to 1.59 inches.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/047,982, filed Mar. 13, 2008. This application is also acontinuation-in-part of U.S. patent application Ser. No. 11/370,732,filed Mar. 7, 2006. The entire disclosure of each of these references ishereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to golf balls comprising a core and acover. The core is a single, solid-layer formed from a rubbercomposition comprising a hydroquinone.

BACKGROUND OF THE INVENTION Hydroquinones

In the golf industry, hydroquinones are commonly used in preparingpolyurea- and polyurethane-based compositions. The use of hydroquinonesin rubber-based golf ball compositions is also known. For example, U.S.Pat. No. 6,339,119 to Ladd et al. discloses a golf ball containing acover layer and a core layer, where the core layer is molded from ascorch retarding composition comprising a scorch retarding peroxide, anelastomeric polymer, and a crosslinking agent. The scorch retardingperoxide typically contains a free radical scavenger selected from thegroup consisting of benzoquinones, hydroquinones, phenols,benzaldehydes, cyclohexadiene-1-ones, and mixtures thereof. The amountof the free radical scavenger in the scorch retarding peroxide ispreferably from about 0.01 parts to about 2 parts per 100 parts of theperoxide by weight.

U.S. Pat. No. 6,919,393 to Mano et al. discloses a solid golf ballcomprising at least one layer of a core, and at least one layer of acover formed on the core, wherein at least one layer including theinnermost layer of the core is formed by vulcanizing a rubbercomposition comprising a base rubber, a co-crosslinking agent, avulcanization initiator and a filler, the core has a center hardness inJIS-C hardness of 40 to 60, a surface hardness in JIS-C hardness of 80to 95 and a hardness difference (B-A) between a hardness in JIS-Chardness at a distance of 5 mm from the center point of the core (B) andthe center hardness (A) of not less than 1 to less than 10. The rubbercompositions for the core can contain a hydroquinone compound.

U.S. Pat. No. 6,956,128 to Higuchi et al. discloses a zinc acrylateparticle composition comprising zinc acrylate satisfying the conditions,(i) that the proportion accounted for by the zinc acrylate particlesmeasuring not less than 300 μm in particle size as determined by the drytype method be not more than 20% by mass of all the particles, (ii) thatthe median of particle sizes as determined by the dry type method be inthe range of 10-300 μm, and (iii) that the ratio of the median (A) ofparticle sizes as determined by the dry type method to the median (B) ofparticle sizes as determined by the wet type method exceed 2, and ananionic surfactant. The acrylic acid used to produce the zinc acrylateparticle composition may contain therein such a polymerization inhibitoras hydroquinone or hydroquinone monomethyl ether.

U.S. Pat. No. 6,767,940 to Voorheis et al. is directed to a golf ballhaving a core and cover, particularly to a golf ball core formed from acomposition including an elastomeric polymer, a free radical initiator,and at least one stable free radical. The composition can furtherinclude one or more free radical scavengers and scorch retarders toincrease the scorch time of the elastomeric polymer. Suitable freeradical scavengers include benzoquinones; hydroquinones; phenols;benzaldehydes; cyclohexadiene-1-ones; and mixtures thereof.

U.S. Patent Application Publication No. 2002/0052253 to Fushihara et al.discloses a one-piece solid golf ball formed from a rubber compositioncomprising a mixture consisting of polybutadiene (a) synthesized usingnickel-containing catalyst and polybutadiene (b) synthesized usingcobalt-containing catalyst and hydroquinone or derivatives thereof as avulcanization stabilizer, wherein a Mooney viscosity and a weight ratioof the polybutadienes (a) and (b), an amount of the vulcanizationstabilizer, a center hardness and surface hardness of the golf ball, anda difference between the maximum hardness and minimum hardness in thegolf ball are adjusted to a specified range. Examples of vulcanizationstabilizers include 2,5-di-t-butylhydroquinone,2,5-di-t-amylhydroquinone, 2,6-dimethylhydroquinone, bromohydroquinone,2,3,5,6-tetrachlorohydroquinone and the like.

U.S. Pat. No. 6,488,597 to Iwami et al. discloses, for example in Table1 on page 5, the use of 2,5-di-t-butylhydroquinone as an antioxidant ina golf ball core formulation.

U.S. Patent Application Publication No. 2007/0213440 to Goguen et al.discloses the use of hydroquinone-containing rubber compositions in avariety of golf ball layers.

Additional background references include U.S. Pat. No. 6,919,393 to Manoet al., U.S. Pat. No. 6,956,128 to Higuchi et al., U.S. PatentApplication Publication No. 2002/0052253 to Fushihara et al., and U.S.Pat. No. 6,488,597 to Iwami et al.

Resilient Cores

The primary source of resilience, as measured by coefficient ofrestitution (“COR”), in commercially available golf balls ispolybutadiene rubber, which is generally used to form all or part of thecore. It is known that the resilience of a golf ball core, at a givencompression, may be increased by forming a core layer from a rubbercomposition comprising an organosulfur compound. However, organosulfurcompounds can be expensive and can cause processing difficulties.

While the use of hydroquinones in rubber golf ball compositions has beendisclosed, there is a need in the industry to broaden the applicabilityof such compositions to particular golf ball constructions havingdesirable spin, feel, and distance properties. The present inventionprovides such golf ball constructions through the use of a solid-singlelayer core formed from a rubber composition comprising a hydroquinone.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is directed to a golf ballconsisting of a core and a cover. The core is a solid, single-layerformed from a rubber composition comprising a base rubber, at least 0.05parts by weight of a free radical initiator per 100 parts of the baserubber, and at least 0.1 parts by weight of a hydroquinone per 100 partsof the base rubber. A ratio (P_(HQ)/P_(FRI)) of the amount of thehydroquinone present in the rubber composition (P_(HQ)), measured inparts by weight, to the amount of free radical initiator present in therubber composition (P_(FRI)), measured in parts by weight, is from 0.05to 2. The core has a center Shore C hardness (H_(CENTER)) and a surfaceShore C hardness (H_(SURFACE)), such that H_(SURFACE)−H_(CENTER)≧25Shore C units.

In another embodiment, the present invention is directed to a golf ballconsisting of a core and a cover. The core is a solid, single-layer corehaving a diameter of from 1.51 inches to 1.59 inches and formed from arubber composition comprising a base rubber, at least 0.05 parts byweight of a free radical initiator per 100 parts of the base rubber, andat least 0.1 parts by weight of a hydroquinone per 100 parts of the baserubber. A ratio (P_(HQ)/P_(FRI)) of the amount of the hydroquinonepresent in the rubber composition (P_(HQ)), measured in parts by weight,to the amount of free radical initiator present in the rubbercomposition (P_(FRI)), measured in parts by weight, is from 0.05 to 2.

DETAILED DESCRIPTION

Golf balls of the present invention include a solid, single-layer coreenclosed by a cover. Thus, golf balls of the present invention includetwo-piece (i.e., solid core and a single-layer cover) and multi-layer(i.e., solid core and a dual- or multi-layer cover) golf balls.

The solid, single-layer cores disclosed herein consist of a single,unitary layer, comprising the entire core from the center of the core toits outer periphery. Solid cores of the present invention are formedfrom a hydroquinone-containing rubber composition and preferably have ahardness gradient of 10 Shore C units or greater, which can be used tocustomize spin, feel, and/or distance characteristics of the golf ball.

Rubber Composition

Rubber compositions of the present invention comprise a base rubberselected from natural and synthetic rubbers, including, but not limitedto, polybutadiene, polyisoprene, ethylene propylene rubber (“EPR”),ethylene propylene diene rubber (“EPDM”), styrene-butadiene rubber,styrenic block copolymer rubbers (such as SI, SIS, SB, SBS, SIBS, andthe like, where “S” is styrene, “I” is isobutylene, and “B” isbutadiene), butyl rubber, halobutyl rubber, polystyrene elastomers,polyethylene elastomers, polyurethane elastomers, polyurea elastomers,metallocene-catalyzed elastomers and plastomers, copolymers ofisobutylene and para-alkylstyrene, halogenated copolymers of isobutyleneand para-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and combinations of two ormore thereof. Diene rubbers are preferred, particularly polybutadiene,styrene-butadiene, and mixtures of polybutadiene with other elastomers,and especially 1,4-polybutadiene having a cis-structure of at least 40%.When the base rubber is a mixture of polybutadiene and at least oneadditional rubber, the amount of polybutadiene in the mixture ispreferably at least 40 wt %, based on the total weight of the mixture.Suitable examples of commercially available polybutadienes include, butare not limited to, Buna CB neodymium catalyzed polybutadiene rubbers,such as Buna CB 23, and Taktene® cobalt catalyzed polybutadiene rubbers,such as Taktene® 220 and 221, commercially available from LANXESS®Corporation; SE BR-1220, commercially available from The Dow ChemicalCompany; Europrene® NEOCIS® BR 40 and BR 60, commercially available fromPolimeri Europa®; UBEPOL-BR® rubbers, commercially available from UBEIndustries, Ltd.; BR 01 commercially available from Japan SyntheticRubber Co., Ltd.; and Neodene neodymium catalyzed high cis polybutadienerubbers, such as Neodene BR 40, commercially available from Karbochem.

Rubber compositions of the present invention include a hydroquinone.Preferred hydroquinones include compounds represented by the followingformula, and hydrates thereof:

-   -   wherein each R₁, R₂, R₃, and R₄ is independently selected from        the group consisting of hydrogen, a halogen group (F, Cl, Br,        I), an alkyl group, a carboxyl group (—COOH) and metal salts        thereof (e.g., —COO⁻M⁺) and esters thereof (—COOR), an acetate        group (—CH₂COOH) and esters thereof (—CH₂COOR), a formyl group        (—CHO), an acyl group (—COR), an acetyl group (—COCH₃), a        halogenated carbonyl group (—COX), a sulfo group (—SO₃H) and        esters thereof (—SO₃R), a halogenated sulfonyl group (—SO₂X), a        sulfino group (—SO₂H), an alkylsulfinyl group (—SOR), a        carbamoyl group (—CONH₂), a halogenated alkyl group, a cyano        group (—CN), an alkoxy group (—OR), a hydroxy group (—OH) and        metal salts thereof (e.g., —O⁻M⁺), an amino group (—NH₂), a        nitro group (—NO₂), an aryl group (e.g., phenyl, tolyl, etc.),        an aryloxy group (e.g., phenoxy, etc.), an arylalkyl group        [e.g., cumyl (—C(CH₃)₂phenyl); benzyl (—CH₂ phenyl)], a nitroso        group (—NO), an acetamido group (—NHCOCH₃), and a vinyl group        (—CH═CH₂).

Particularly preferred hydroquinones include compounds represented bythe following formula, and hydrates thereof:

-   -   wherein each R₁, R₂, R₃, and R₄ is independently selected from        the group consisting of: a metal salt of a carboxyl group (e.g.,        —COO⁻M⁺), an acetate group (—CH₂COOH) and esters thereof        (—CH₂COOR), a hydroxy group (—OH), a metal salt of a hydroxy        group (e.g., —O⁻M⁺), an amino group (—NH₂), a nitro group        (—NO₂), an aryl group (e.g., phenyl, tolyl, etc.), an aryloxy        group (e.g., phenoxy, etc.), an arylalkyl group [e.g., cumyl        (—C(CH₃)₂phenyl); benzyl (—CH₂ phenyl)], a nitroso group (—NO),        an acetamido group (—NHCOCH₃), and a vinyl group (—CH═CH₂).

In a particular embodiment, the hydroquinone is selected from compoundsrepresented by one of the above formulas, except2,5-di-t-butylhydroquinone.

Examples of particularly suitable hydroquinones include, but are notlimited to, hydroquionone; tetrachlorohydroquinone;2-chlorohydroquionone; 2-bromohydroquinone; 2,5-dichlorohydroquinone;2,5-dibromohydroquinone; tetrabromohydroquinone; 2-methylhydroquinone;2-t-butylhydroquinone; 2,5-di-t-amylhydroquinone; and2-(2-chlorophenyl)hydroquinone hydrate. Hydroquinone andtetrachlorohydroquinone are particularly preferred, and even moreparticularly preferred is 2-(2-chlorophenyl)hydroquinone hydrate.

Rubber compositions of the present invention may include a combinationof two or more hydroquinones, each of which is independently selectedfrom compounds represented by one of the above formulas, or acombination of one or more hydroquinones with one or more chemicalcompounds selected from the group consisting of benzoquinones,quinhydrones, catechols, and resorcinols.

The present invention is not limited by a particular method for addingthe hydroquinone to the rubber composition. The hydroquinone can beadded as part of a masterbatch or in the neat form as a liquid or solid.

The hydroquinone is generally present in the rubber composition in anamount of at least 0.05 parts by weight or at least 0.1 parts by weightor at least 0.15 parts by weight or at least 0.2 parts by weight per 100parts of the base rubber, or an amount within the range having a lowerlimit of 0.05 parts or 0.1 parts or 0.15 parts or 0.25 parts or 0.3parts or 0.375 parts by weight per 100 parts of the base rubber, and anupper limit of 0.5 parts or 0.7 parts or 1 part or 1.5 parts or 2 partsor 3 parts by weight per 100 parts of the base rubber. In a particularembodiment, a ratio (P_(HQ)/P_(FRI)) of the amount (P_(HQ)) of thehydroquinone present in the rubber composition, measured in parts byweight per 100 parts of the base rubber, to the amount (P_(FRI)) of freeradical initiator present in the rubber composition, measured in partsby weight per 100 parts of the base rubber, is from 0.05 to 2. Inanother embodiment, P_(HQ)/P_(FRI) is at least 0.05 and less than 0.5.In another embodiment, P_(HQ)/P_(FRI) is at least 0.2 and less than 0.5.In another embodiment, P_(HQ)/P_(FRI) is at least 0.25 and less than0.5. In yet another embodiment, P_(HQ)/P_(FRI) is within the rangehaving a lower limit of 0.05 or 0.2 or 0.25 and an upper limit of 0.4 or0.45 or 0.5 or 2.

Rubber compositions of the present invention preferably comprise a freeradical initiator selected from organic peroxides, high energy radiationsources capable of generating free radicals, and combinations thereof.Suitable organic peroxides include, but are not limited to, dicumylperoxide; n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. In aparticular embodiment, the free radical initiator is dicumyl peroxide,including, but not limited to Perkadox® BC, commercially available fromAkzo Nobel. Peroxide free radical initiators are generally present inthe rubber composition in an amount of at least 0.05 parts by weight per100 parts of the base rubber, or an amount within the range having alower limit of 0.05 parts or 0.1 parts or 1 part or 1.25 parts or 1.5parts by weight per 100 parts of the base rubber, and an upper limit of2.5 parts or 3 parts or 5 parts or 6 parts or 10 parts or 15 parts byweight per 100 parts of the base rubber.

Coagents are commonly used with peroxides to increase the state of cure.Suitable coagents include, but are not limited to, metal salts ofunsaturated carboxylic acids having from 3 to 8 carbon atoms;unsaturated vinyl compounds and polyfunctional monomers (e.g.,trimethylolpropane trimethacrylate); phenylene bismaleimide; andcombinations thereof. Particular examples of suitable metal saltsinclude, but are not limited to, one or more metal salts of acrylates,diacrylates, methacrylates, and dimethacrylates, wherein the metal isselected from magnesium, calcium, zinc, aluminum, lithium, and nickel.In a particular embodiment, the coagent is selected from zinc salts ofacrylates, diacrylates, methacrylates, and dimethacrylates. In anotherparticular embodiment, the coagent is zinc diacrylate. When the coagentis zinc diacrylate and/or zinc dimethacrylate, the coagent is typicallyincluded in the rubber composition in an amount within the range havinga lower limit of 1 or 5 or 10 or 15 or 19 or 20 parts by weight per 100parts of the base rubber, and an upper limit of 24 or 25 or 30 or 35 or40 or 45 or 50 or 60 parts by weight per 100 parts of the base rubber.When one or more less active coagents are used, such as zincmonomethacrylate and various liquid acrylates and methacrylates, theamount of less active coagent used may be the same as or higher than forzinc diacrylate and zinc dimethacrylate coagents. The desiredcompression may be obtained by adjusting the amount of crosslinking,which can be achieved, for example, by altering the type and amount ofcoagent.

Curing agents may also be used in rubber compositions of the presentinvention. Curing agents include, but are not limited to, sulfur;N-oxydiethylene 2-benzothiazole sulfenamide;N,N-di-ortho-tolylguanidine; bismuth dimethyldithiocarbamate;N-cyclohexyl 2-benzothiazole sulfenamide; N,N-diphenylguanidine;4-morpholinyl-2-benzothiazole disulfide; dipentamethylenethiuramhexasulfide; thiuram disulfides; mercaptobenzothiazoles; sulfenamides;dithiocarbamates; thiuram sulfides; guanidines; thioureas; xanthates;dithiophosphates; aldehyde-amines; dibenzothiazyl disulfide;tetraethylthiuram disulfide; tetrabutylthiuram disulfide; andcombinations thereof.

High energy radiation sources capable of generating free radicalsinclude, but are not limited to, electron beams, ultra-violet radiation,gamma radiation, X-ray radiation, infrared radiation, heat, andcombinations thereof.

Rubber compositions of the present invention optionally contain one ormore antioxidants. When antioxidants are included in the rubbercomposition, the amount of free radical initiator used may be as high orhigher than the amounts disclosed herein. Suitable antioxidants include,for example, dihydroquinoline antioxidants, amine type antioxidants, andphenolic type antioxidants.

Rubber compositions of the present invention optionally contain one ormore fillers to adjust the density and/or specific gravity of the coreor cover. Exemplary fillers include, but are not limited to,precipitated hydrated silica, clay, talc, asbestos, glass fibers, aramidfibers, mica, calcium metasilicate, barium sulfate, zinc sulfide,lithopone, silicates, silicon carbide, diatomaceous earth, polyvinylchloride, carbonates (e.g., calcium carbonate, zinc carbonate, bariumcarbonate, and magnesium carbonate), metals (e.g., titanium, tungsten,aluminum, bismuth, nickel, molybdenum, iron, lead, copper, boron,cobalt, beryllium, zinc, and tin), metal alloys (e.g., steel, brass,bronze, boron carbide whiskers, and tungsten carbide whiskers), metaloxides (e.g., zinc oxide, iron oxide, aluminum oxide, titanium oxide,magnesium oxide, zirconium oxide, and tin oxide), particulatecarbonaceous materials (e.g., graphite, carbon black, cotton flock,natural bitumen, cellulose flock, and leather fiber), microballoons(e.g., glass and ceramic), fly ash, regrind, nanofillers andcombinations thereof. The amount of particulate material(s) present inrubber compositions of the present invention is typically within therange having a lower limit of 5 parts or 10 parts by weight per 100parts of the base rubber, and an upper limit of 30 parts or 50 parts or100 parts by weight per 100 parts of the base rubber.

Rubber compositions of the present invention optionally contain one ormore additives selected from processing aids, processing oils,plasticizers, coloring agents, fluorescent agents, chemical blowing andfoaming agents, defoaming agents, stabilizers, softening agents, impactmodifiers, and the like. The amount of additive(s) typically present inrubber compositions of the present invention is typically within therange having a lower limit of 0 parts by weight per 100 parts of thebase rubber and an upper limit of 20 parts or 50 parts or 100 parts or150 parts by weight per 100 parts of the base rubber.

In one embodiment of the present invention, the rubber compositioncontains a conventional soft and fast agent. The conventional soft andfast agent is optionally used in an amount within a range having a lowerlimit of 0.1 or 0.2 or 0.5 phr and an upper limit of 2 or 3 or 5 phr. Asused herein, “soft and fast agent” means any compound or a blend thereofthat is capable of making a core 1) softer (have a lower compression) ata constant COR and/or 2) faster (have a higher COR at equalcompression), when compared to a core equivalently prepared without asoft and fast agent. Suitable conventional soft and fast agents include,but are not limited to, those selected from organosulfur andmetal-containing organosulfur compounds, organic sulfur compounds,including mono, di, and polysulfides, thiol, and mercapto compounds,inorganic sulfide compounds, Group VIA compounds, substituted orunsubstituted aromatic organic compounds that do not contain sulfur ormetal, aromatic organometallic compounds, and mixtures thereof.Particularly suitable soft and fast agents include, but are not limitedto, zinc pentachlorothiophenol, pentachlorothiophenol, ditolyldisulfide, diphenyl disulfide, dixylyl disulfide, and mixtures thereof.The soft and fast agent component may also be a blend of an organosulfurcompound and an inorganic sulfide compound. Suitable organosulfurcompounds are further disclosed, for example, in U.S. Pat. Nos.6,635,716, 6,919,393, 7,005,479 and 7,148,279, the entire disclosures ofwhich are hereby incorporated herein by reference.

In another embodiment, the rubber composition is substantially free oforganosulfur compounds. “Substantially free,” as used herein, means thatthe rubber composition does not contain an organosulfur compound, orincludes one or more organosulfur compounds in an amount of less than0.01 parts by weight per 100 parts of the base rubber.

Suitable types and amounts of rubber, initiator, coagent, curing agent,antioxidant, filler, and additive are more fully disclosed, for example,in U.S. Pat. Nos. 6,566,483, 6,695,718, 6,939,907, 7,041,721 and7,138,460, the entire disclosures of which are hereby incorporatedherein by reference.

A non-limiting example of a preferred rubber formulation is shown inTable 1 below.

TABLE 1 SE BR-1220* 100 (parts by weight) zinc diacrylate 40 (parts byweight) Perkadox ® BC** 1.25 (parts by weight) zinc oxide 5 (parts byweight) zinc pentachlorothiophenol 0.5 (parts by weight) hydroquinone0.75 (parts by weight) filler *** (parts by weight) *SE BR-1220 is ahigh cis-1,4 polybutadiene commercially available from The Dow ChemicalCompany. **Perkadox ® BC is a peroxide free radical initiatorscommercially available from Akzo Nobel. ***The amount of filler used canbe adjusted to hit target specific gravity.

Golf Ball Applications

A golf ball having a solid, single-layer core and a cover enclosing thecore is disclosed. The core is formed from a hydroquinone-containingrubber composition, as disclosed above, and generally has a diameterwithin a range having a lower limit of 1.00 or 1.25 or 1.40 or 1.45 or1.50 or 1.51 or 1.52 or 1.53 inches and an upper limit of 1.54 or 1.55or 1.56 or 1.57 or 1.58 or 1.59 or 1.60 or 1.62 or 1.63 or 1.66 inches.In a particularly preferred embodiment, the core has a diameter of about1.53 inches.

The core preferably has a center hardness of 70 Shore C or less, or 65Shore C or less, or a center hardness within a range having a lowerlimit of 30 or 40 or 45 or 50 Shore C and an upper limit of 55 or 60 or65 or 70 or 75 or 80 Shore C.

The surface hardness of the core is preferably 80 Shore C or greater, orgreater than 80 Shore C, or 85 Shore C or greater, or greater than 85Shore C, or 87 Shore C or greater, or 90 Shore C or greater, or within arange having a lower limit of 80 or 85 or 90 Shore C and an upper limitof 95 Shore C or 100 Shore C or 60 Shore D or 65 Shore D or 70 Shore D.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut, made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight of the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within ±10.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center mark.

The surface hardness of a golf ball layer is obtained from the averageof a number of measurements taken from opposing hemispheres, taking careto avoid making measurements on the parting line of the core or onsurface defects, such as holes or protrusions. Hardness measurements aremade pursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plasticby Means of a Durometer.” Because of the curved surface, care must betaken to insure that the golf ball or golf ball subassembly is centeredunder the durometer indentor before a surface hardness reading isobtained. A calibrated, digital durometer, capable of reading to 0.1hardness units is used for all hardness measurements and is set to takehardness readings at 1 second after the maximum reading is obtained. Thedigital durometer must be attached to, and its foot made parallel to,the base of an automatic stand. The weight on the durometer and attackrate conform to ASTM D-2240.

In a particular embodiment, the surface hardness of the core is greaterthan or equal to the center hardness of the core. In another particularembodiment, the core has a positive hardness gradient wherein thedifference between the surface hardness of the core (H_(SURFACE)) andthe center hardness of the core (H_(CENTER)) is 10 Shore C units orgreater, or 15 Shore C units or greater, or 20 Shore C units or greater,or 25 Shore C units or greater, or 30 Shore C units or greater, or 35Shore C units or greater, or 40 Shore C units or greater, or 45 Shore Cunits or greater. In another particular embodiment, the core has apositive hardness gradient wherein the difference between the surfacehardness of the core (H_(SURFACE)) and the center hardness of the core(H_(CENTER)) is within a range having a lower limit of 20 or 25 or 30 or35 or 40 Shore C units and an upper limit of 45 or 50 or 55 Shore Cunits.

A hardness gradient of a core is defined by hardness measurements madeat the surface and center of the core. For purposes of the presentinvention, “negative” and “positive” refer to the result of subtractingthe hardness value at the innermost portion of the golf ball componentfrom the hardness value at the outer surface of the component. Forexample, if the outer surface of a solid core has a lower hardness valuethan the center (i.e., the surface is softer than the center), thehardness gradient will be deemed a “negative” gradient. In measuring thehardness gradient of a core, the center hardness is first determinedaccording to the procedure above for obtaining the center hardness of acore. Once the center of the core is marked and the hardness thereof isdetermined, hardness measurements at any distance from the center of thecore may be measured by drawing a line radially outward from the centermark, and measuring and marking the distance from the center, typicallyin 2 mm increments. All hardness measurements performed on a planepassing through the geometric center are performed while the core isstill in the holder and without having disturbed its orientation, suchthat the test surface is constantly parallel to the bottom of theholder. The hardness difference from any predetermined location on thecore is calculated as the average surface hardness minus the hardness atthe appropriate reference point, e.g., at the center of the core for asingle, solid core, such that a core surface softer than its center willhave a negative hardness gradient. Hardness gradients are disclosed morefully, for example, in U.S. patent application Ser. Nos. 11/832,163,filed on Aug. 1, 2007; 11/939,632, filed on Nov. 14, 2007; 11/939,634,filed on Nov. 14, 2007; 11/939,635, filed on Nov. 14, 2007; and11/939,637, filed on Nov. 14, 2007; the entire disclosure of each ofthese references is hereby incorporated herein by reference.

The weight distribution of cores disclosed herein can be varied toachieve certain desired parameters, such as spin rate, compression, andinitial velocity.

Golf ball cores of the present invention preferably have a compressionof 110 or less, or 90 or less, or 80 or less, or 75 or less, or 70 orless, or 65 or less, or 60 or less, or 50 or less, or a compression offrom 50 to 90, or from 60 to 85, or from 60 to 80, or from 65 to 80, oran overall compression of about 70.

Compression is an important factor in golf ball design. For example, thecompression of the core can affect the ball's spin rate off the driverand the feel. As disclosed in Jeff Dalton's Compression by Any OtherName, Science and Golf IV, Proceedings of the World Scientific Congressof Golf (Eric Thain ed., Routledge, 2002) (“J. Dalton”), severaldifferent methods can be used to measure compression, including Atticompression, Riehle compression, load/deflection measurements at avariety of fixed loads and offsets, and effective modulus. For purposesof the present invention, “compression” refers to Atti compression andis measured according to a known procedure, using an Atti compressiontest device, wherein a piston is used to compress a ball against aspring. The travel of the piston is fixed and the deflection of thespring is measured. The measurement of the deflection of the spring doesnot begin with its contact with the ball; rather, there is an offset ofapproximately the first 1.25 mm (0.05 inches) of the spring'sdeflection. Very low stiffness cores will not cause the spring todeflect by more than 1.25 mm and therefore have a zero compressionmeasurement. The Atti compression tester is designed to measure objectshaving a diameter of 1.680 inches; thus, smaller objects, such as golfball cores, must be shimmed to a total height of 1.680 inches to obtainan accurate reading. Conversion from Atti compression to Riehle (cores),Riehle (balls), 100 kg deflection, 130-10 kg deflection or effectivemodulus can be carried out according to the formulas given in J. Dalton.Golf ball cores of the present invention typically have a coefficient ofrestitution (“COR”) at 125 ft/s of at least 0.750, or at least 0.775 orat least 0.780, or at least 0.782, or at least 0.785, or at least 0.787,or at least 0.790, or at least 0.795, or at least 0.798, or at least0.800.

COR, as used herein, is determined according to a known procedurewherein a golf ball or golf ball subassembly (e.g., a golf ball core) isfired from an air cannon at two given velocities and calculated at avelocity of 125 ft/s. Ballistic light screens are located between theair cannon and the steel plate at a fixed distance to measure ballvelocity. As the ball travels toward the steel plate, it activates eachlight screen, and the time at each light screen is measured. Thisprovides an incoming transit time period inversely proportional to theball's incoming velocity. The ball impacts the steel plate and reboundsthough the light screens, which again measure the time period requiredto transit between the light screens. This provides an outgoing transittime period inversely proportional to the ball's outgoing velocity. CORis then calculated as the ratio of the outgoing transit time period tothe incoming transit time period, COR=V_(out)/V_(in)=T_(in)/T_(out).

Cores of the present invention are enclosed with a cover, which may be asingle-, dual-, or multi-layer cover, preferably having an overallthickness within the range having a lower limit of 0.01 inches or 0.02inches or 0.025 inches or 0.03 inches or 0.04 inches or 0.045 inches or0.05 inches or 0.06 inches and an upper limit of 0.07 inches or 0.075inches or 0.08 inches or 0.09 inches or 0.1 inches or 0.15 inches or 0.2inches or 0.3 inches or 0.5 inches. Dual and multilayer covers have aninner cover layer and an outer cover layer, and multilayer coversadditionally have at least one intermediate cover layer disposed betweenthe inner cover layer and the outer cover layer. Inner cover layers ofthe present invention preferably have a thickness within the rangehaving a lower limit of 0.01 inches or 0.02 inches or 0.025 inches andan upper limit of 0.05 inches or 0.15 inches or 0.2 inches. Outer coverlayers of the present invention preferably have a thickness of 0.01inches or 0.02 inches or 0.025 inches and an upper limit of 0.05 inchesor 0.15 inches or 0.2 inches. Intermediate cover layer(s) of the presentinvention preferably have a thickness of 0.01 inches or 0.02 inches or0.025 inches and an upper limit of 0.05 inches or 0.15 inches or 0.2inches.

The cover material is preferably a tough, cut-resistant material,selected based on the desired performance characteristics. Suitablecover materials for the golf balls disclosed herein include, but are notlimited to, ionomer resins and blends thereof (e.g., Surlyn® ionomerresins and DuPont® HPF 1000 and HPF 2000, commercially available from E.I. du Pont de Nemours and Company; Iotek® ionomers, commerciallyavailable from ExxonMobil Chemical Company; Amplify® 10 ionomers ofethylene acrylic acid copolymers, commercially available from The DowChemical Company; and Clarix® ionomer resins, commercially availablefrom A. Schulman Inc.); polyurethanes; polyureas; copolymers and hybridsof polyurethane and polyurea; polyethylene, including, for example, lowdensity polyethylene, linear low density polyethylene, and high densitypolyethylene; polypropylene; rubber-toughened olefin polymers; acidcopolymers, e.g., (meth)acrylic acid, which do not become part of anionomeric copolymer; plastomers; flexomers; styrene/butadiene/styreneblock copolymers; styrene/ethylenebutylene/styrene block copolymers;dynamically vulcanized elastomers; ethylene vinyl acetates; ethylenemethyl acrylates; polyvinyl chloride resins; polyamides, amide-esterelastomers, and graft copolymers of ionomer and polyamide, including,for example, Pebax® thermoplastic polyether block amides, commerciallyavailable from Arkema Inc; crosslinked transpolyisoprene and blendsthereof; polyester-based thermoplastic elastomers, such as Hytrel®,commercially available from E. I. du Pont de Nemours and Company;polyurethane-based thermoplastic elastomers, such as Elastollan®,commercially available from BASF; synthetic or natural vulcanizedrubber; and combinations thereof. Suitable cover materials andconstructions also include, but are not limited to, those disclosed inU.S. Pat. Nos. 6,117,025, 6,767,940, and 6,960,630, the entiredisclosures of which are hereby incorporated herein by reference.

Compositions comprising an ionomer or a blend of two or more ionomersare particularly suitable for forming the inner cover layer indual-layer covers. Preferred ionomeric compositions include:

-   -   (a) a composition comprising a “high acid ionomer” (i.e., having        an acid content of greater than 16 wt %), such as Surlyn 8150®;    -   (b) a composition comprising a high acid ionomer and a maleic        anhydride-grafted non-ionomeric polymer (e.g., Fusabond® maleic        anhydride-grafted metallocene-catalyzed ethylene-butene        copolymers). A particularly preferred blend of high acid ionomer        and maleic anhydride-grafted polymer is a 84 wt %/16 wt % blend        of Surlyn 8150® and Fusabond®. Blends of high acid ionomers with        maleic anhydride-grafted polymers are further disclosed, for        example, in U.S. Pat. Nos. 6,992,135 and 6,677,401, the entire        disclosures of which are hereby incorporated herein by        reference;    -   (c) a composition comprising a 50/45/5 blend of Surlyn®        8940/Surlyn® 9650/Nucrel® 960, preferably having a material        hardness of from 80 to 85 Shore C;    -   (d) a composition comprising a 50/25/25 blend of Surlyn®        8940/Surlyn® 9650/Surlyn® 9910, preferably having a material        hardness of about 90 Shore C;    -   (e) a composition comprising a 50/50 blend of Surlyn®        8940/Surlyn® 9650, preferably having a material hardness of        about 86 Shore C;    -   (f) a composition comprising a blend of Surlyn® 7940/Surlyn®        8940, optionally including a melt flow modifier;    -   (g) a composition comprising a blend of a first high acid        ionomer and a second high acid ionomer, wherein the first high        acid ionomer is neutralized with a different cation than the        second high acid ionomer (e.g., 50/50 blend of Surlyn® 8150 and        Surlyn® 9150), optionally including one or more melt flow        modifiers such as an ionomer, ethylene-acid copolymer or ester        terpolymer; and    -   (h) a composition comprising a blend of a first high acid        ionomer and a second high acid ionomer, wherein the first high        acid ionomer is neutralized with a different cation than the        second high acid ionomer, and from 0 to 10 wt % of an        ethylene/acid/ester ionomer wherein the ethylene/acid/ester        ionomer is neutralized with the same cation as either the first        high acid ionomer or the second high acid ionomer or a different        cation than the first and second high acid ionomers (e.g., a        blend of 40-50 wt % Surlyn® 8140, 40-50 wt % Surlyn® 9120, and        0-10 wt % Surlyn® 6320).

Surlyn 8150®, Surlyn® 8940, and Surlyn® 8140 are different grades ofE/MAA copolymer in which the acid groups have been partially neutralizedwith sodium ions. Surlyn 9650, Surlyn® 9910, Surlyn® 9150, and Surlyn®9120 are different grades of E/MAA copolymer in which the acid groupshave been partially neutralized with zinc ions. Surlyn® 7940 is an E/MAAcopolymer in which the acid groups have been partially neutralized withlithium ions. Surlyn® 6320 is a very low modulus magnesium ionomer witha medium acid content. Nucrel® 960 is an E/MAA copolymer resin nominallymade with 15 wt % methacrylic acid. Surlyn® ionomers, Fusabond®copolymers, and Nucrel® copolymers are commercially available from E. I.du Pont de Nemours and Company.

Non-limiting examples of particularly preferred ionomeric cover layerformulations are shown in Table 2 below.

TABLE 2 Shore C Hardness Cover Layer Surlyn ® 8150, Fusabond ®, atMaterial wt % wt % 10 Days 1 89 11 91.2 2 84 16 89.8 3 84 16 90.4 4 8416 89.6 5 81 19 88.9 6 80 20 89.1 7 78 22 88.1 8 76 24 87.6 9 76 24 87.210 73 27 86.6 11 71 29 86.7 12 67 33 84.0Ionomeric cover compositions can be blended with non-ionic thermoplasticresins, particularly to manipulate product properties. Examples ofsuitable non-ionic thermoplastic resins include, but are not limited to,polyurethane, poly-ether-ester, poly-amide-ether, polyetherurea,thermoplastic polyether block amides (e.g., Pebax® block copolymers,commercially available from Arkema Inc.), styrene-butadiene-styreneblock copolymers, styrene(ethylenebutylene)-styrene block copolymers,polyamides, polyesters, polyolefins (e.g., polyethylene, polypropylene,ethylene-propylene copolymers, polyethylene-(meth)acrylate,plyethylene(meth)acrylic acid, functionalized polymers with maleicanhydride grafting, Fusabond® functionalized olefins commerciallyavailable from E. I. du Pont de Nemours and Company, functionalizedpolymers with epoxidation, elastomers (e.g., ethylene propylene dienemonomer rubber, metallocene-catalyzed polyolefin) and ground powders ofthermoset elastomers.

Suitable ionomeric cover materials are further disclosed, for example,in U.S. Pat. Nos. 6,653,382, 6,756,436, 6,894,098, 6,919,393, and6,953,820, the entire disclosures of which are hereby incorporated byreference.

Polyurethanes, polyureas, and blends and hybrids ofpolyurethane/polyurea are particularly suitable for forming the outercover layer in dual-layer covers. When used as cover layer materials,polyurethanes and polyureas can be thermoset or thermoplastic. Thermosetmaterials can be formed into golf ball layers by conventional casting orreaction injection molding techniques. Thermoplastic materials can beformed into golf ball layers by conventional compression or injectionmolding techniques. In embodiments of the present invention wherein agolf ball having a single layer cover is provided, the cover layermaterial is preferably selected from polyurethane and polyurea. Inembodiments of the present invention wherein a golf ball having a dualcover is provided, the inner cover layer is preferably a high modulusthermoplastic, and the outer cover layer is preferably selected frompolyurethane and polyurea.

Suitable polyurethane cover materials are further disclosed in U.S. Pat.Nos. 5,334,673, 6,506,851, 6,756,436, and 7,105,623, the entiredisclosures of which are hereby incorporated herein by reference.Suitable polyurea cover materials are further disclosed in U.S. Pat.Nos. 5,484,870 and 6,835,794, the entire disclosures of which are herebyincorporated herein by reference. Suitable polyurethane-urea covermaterials include polyurethane/polyurea blends and copolymers comprisingurethane and urea segments, as disclosed in U.S. Patent ApplicationPublication No. 2007/0117923, the entire disclosure of which is herebyincorporated herein by reference.

Golf ball cover compositions may include a flow modifier, such as, butnot limited to, Nucrel® acid copolymer resins, and particularly Nucrel®960. Nucrel® acid copolymer resins are commercially available from E. I.du Pont de Nemours and Company.

Cover compositions may also include one or more filler(s), such as thefillers given above for rubber compositions of the present invention(e.g., titanium dioxide, barium sulfate, etc.), and/or additive(s), suchas coloring agents, fluorescent agents, whitening agents, antioxidants,dispersants, UV absorbers, light stabilizers, plasticizers, surfactants,compatibility agents, foaming agents, reinforcing agents, releaseagents, and the like.

Additional suitable cover materials are disclosed, for example, in U.S.Patent Application Publication No. 2005/0164810, U.S. Pat. No.5,919,100, and PCT Publications WO00/23519 and WO00/29129, the entiredisclosures of which are hereby incorporated herein by reference.

In a particular embodiment, the cover is a single layer preferablyformed from an ionomeric composition. The single layer cover preferablyhas a surface hardness of 65 Shore D or less, or 60 Shore D or less, or45 Shore D or less, or 40 Shore D or less, or from 25 Shore D to 40Shore D, or from 30 Shore D to 40 Shore D and a thickness within a rangehaving a lower limit of 0.010 or 0.015 or 0.020 or 0.025 or 0.030 or0.055 or 0.060 inches and an upper limit of 0.065 or 0.080 or 0.090 or0.100 or 0.110 or 0.120 or 0.140 inches.

In another particular embodiment, the cover is a two-layer coverconsisting of an inner cover layer and an outer cover layer. In aparticular aspect of this embodiment, the surface hardness of the coreis greater than the material hardness of the inner cover layer. Inanother particular aspect of this embodiment, the surface hardness ofthe core is greater than the material hardness of both the inner coverlayer and the outer cover layer.

The inner cover layer is preferably formed from an ionomeric compositionand preferably has a surface hardness of 60 Shore D or greater, or 65Shore D or greater, or a surface hardness within a range having a lowerlimit of 30 or 40 or 55 or 60 or 65 Shore D and an upper limit of 66 or68 or 70 or 75 Shore D, and a thickness within a range having a lowerlimit of 0.010 or 0.015 or 0.020 or 0.030 inches and an upper limit of0.035 or 0.040 or 0.045 or 0.050 or 0.055 or 0.075 or 0.080 or 0.100 or0.110 or 0.120 inches. The inner cover layer composition preferably hasa material hardness of 95 Shore C or less, or less than 95 Shore C, or92 Shore C or less, or 90 Shore C or less, or 85 Shore C or less, or hasa material hardness within a range having a lower limit of 70 or 75 or80 or 82 or 84 Shore C and an upper limit of 85 or 86 or 90 or 92 or 95Shore C. The outer cover layer is preferably formed from a castable orreaction injection moldable polyurethane, polyurea, or copolymer orhybrid of polyurethane/polyurea. Such cover material is preferablythermosetting, but may be thermoplastic. The outer cover layercomposition preferably has a material hardness of 85 Shore C or less, or45 Shore D or less, or 40 Shore D or less, or from 25 Shore D to 40Shore D, or from 30 Shore D to 40 Shore D. The outer cover layerpreferably has a surface hardness within a range having a lower limit of20 or 30 or 35 or 40 Shore D and an upper limit of 52 or 58 or 60 or 65or 70 or 72 or 75 Shore D. The outer cover layer preferably has athickness within a range having a lower limit of 0.010 or 0.015 or 0.025inches and an upper limit of 0.035 or 0.040 or 0.045 or 0.050 or 0.055or 0.075 or 0.080 or 0.115 inches. The two-layer cover preferably has anoverall thickness within a range having a lower limit of 0.010 or 0.015or 0.020 or 0.025 or 0.030 or 0.055 or 0.060 inches and an upper limitof 0.065 or 0.075 or 0.080 or 0.090 or 0.100 or 0.110 or 0.120 or 0.140inches.

For purposes of the present disclosure, material hardness is measuredaccording to ASTM D2240 and generally involves measuring the hardness ofa flat “slab” or “button” formed of the material. It should beunderstood that there is a fundamental difference between “materialhardness” and “hardness as measured directly on a golf ball.” Hardnessas measured directly on a golf ball (or other spherical surface)typically results in a different hardness value than material hardness.This difference in hardness values is due to several factors including,but not limited to, ball construction (i.e., core type, number of coreand/or cover layers, etc.), ball (or sphere) diameter, and the materialcomposition of adjacent layers. It should also be understood that thetwo measurement techniques are not linearly related and, therefore, onehardness value cannot easily be correlated to the other. Unless statedotherwise, the hardness values given herein for cover materials arematerial hardness values measured according to ASTM D2240, with allvalues reported following 10 days of aging at 50% relative humidity and23° C.

Golf balls of the present invention optionally include one or moreintermediate layer(s) disposed between the core and the cover. Whenpresent, the overall thickness of the intermediate layer(s) is generallywithin the range having a lower limit of 0.01 inches or 0.05 inches or0.1 inches and an upper limit of 0.3 inches or 0.35 inches or 0.4inches. Suitable intermediate layer materials include, but are notlimited to, natural rubbers, balata, gutta-percha, cis-polybutadienes,trans-polybutadienes, synthetic polyisoprenes, polyoctenamers,styrene-propylene-diene rubbers, metallocene rubbers, styrene-butadienerubbers, ethylene-propylenes, chloroprene rubbers, acrylonitrilerubbers, acrylonitrile-butadiene rubbers, styrene-ethylene blockcopolymers, maleic anhydride or succinate modified metallocene catalyzedethylene copolymers, polypropylene resins, ionomer resins, polyamides,polyesters, polyurethanes, polyureas, chlorinated polyethylenes,polysulfide rubbers, fluorocarbons, and combinations thereof.

A moisture vapor barrier layer is optionally employed between the coreand the cover. Moisture vapor barrier layers are further disclosed, forexample, in U.S. Pat. Nos. 6,632,147, 6,932,720, 7,004,854, and7,182,702, the entire disclosures of which are hereby incorporatedherein by reference.

Golf balls of the present invention preferably have an overall diameterwithin the range having a lower limit of 1.60 or 1.62 or 1.66 inches andan upper limit of 1.69 or 1.74 or 1.80 inches. More preferably, golfballs of the present invention have an overall diameter of 1.68 inches.Golf balls of the present invention typically have a compression withina range having a lower limit of 40 or 50 or 60 and an upper limit of 100or 105 or 110 or 120. Golf balls of the present invention preferablyhave a COR at 125 ft/s of 0.700 or greater, or 0.750 or greater, or0.780 or greater, or 0.790 or greater.

Golf balls of the present invention will typically have dimple coverageof 60% or greater, preferably 65% or greater, and more preferably 75% orgreater.

The United States Golf Association specifications limit the minimum sizeof a competition golf ball to 1.680 inches. There is no specification asto the maximum diameter, and golf balls of any size can be used forrecreational play. Golf balls of the present invention can have anoverall diameter of any size. The preferred diameter of the present golfballs is from 1.680 inches to 1.800 inches. More preferably, the presentgolf balls have an overall diameter of from 1.680 inches to 1.760inches, and even more preferably from 1.680 inches to 1.740 inches.

Golf balls of the present invention preferably have a moment of inertia(“MOI”) of 70-95 g·cm², preferably 75-93 g·cm², and more preferably76-90 g·cm². For low MOI embodiments, the golf ball preferably has anMOI of 85 g·cm² or less, or 83 g·cm² or less. For high MOI embodiment,the golf ball preferably has an MOI of 86 g·cm² or greater, or 87 g·cm²or greater. MOI is measured on a model MOI-005-104 Moment of InertiaInstrument manufactured by Inertia Dynamics of Collinsville, Conn. Theinstrument is connected to a PC for communication via a COMM port and isdriven by MOI Instrument Software version #1.2.

Suitable golf ball constructions and materials are further disclosed,for example, in U.S. Patent Application Publication Nos. 2003/0144087and 2005/0164810, U.S. Pat. Nos. 5,688,119 and 5,919,100, and PCTPublications WO00/23519 and WO00/29129. The entire disclosure of each ofthese references is hereby incorporated herein by reference.

The present invention is not limited by any particular process forforming the golf ball layer(s). It should be understood that thelayer(s) can be formed by any suitable technique, including injectionmolding, compression molding, casting, and reaction injection molding.

When injection molding is used, the composition is typically in apelletized or granulated form that can be easily fed into the throat ofan injection molding machine wherein it is melted and conveyed via ascrew in a heated barrel at temperatures of from 150° F. to 600° F.,preferably from 200° F. to 500° F. The molten composition is ultimatelyinjected into a closed mold cavity, which may be cooled, at ambient orat an elevated temperature, but typically the mold is cooled to atemperature of from 50° F. to 70° F. After residing in the closed moldfor a time of from 1 second to 300 seconds, preferably from 20 secondsto 120 seconds, the core and/or core plus one or more additional core orcover layers is removed from the mold and either allowed to cool atambient or reduced temperatures or is placed in a cooling fluid such aswater, ice water, dry ice in a solvent, or the like.

When compression molding is used to form a core, the composition isfirst formed into a preform or slug of material, typically in acylindrical or roughly spherical shape at a weight slightly greater thanthe desired weight of the molded core. Prior to this step, thecomposition may be first extruded or otherwise melted and forced througha die after which it is cut into a cylindrical preform. It is thatpreform that is then placed into a compression mold cavity andcompressed at a mold temperature of from 150° F. to 400° F., preferablyfrom 250° F. to 400° F., and more preferably from 300° F. to 400° F.When compression molding a cover layer, half-shells of the cover layermaterial are first formed via injection molding. A core is then enclosedwithin two half shells, which is then placed into a compression moldcavity and compressed.

Reaction injection molding processes are further disclosed, for example,in U.S. Pat. Nos. 6,083,119, 7,338,391, 7,282,169, 7,281,997 and U.S.Patent Application Publication No. 2006/0247073, the entire disclosuresof which are hereby incorporated herein by reference.

In addition to the materials disclosed above, any of the core or coverlayers may comprise one or more of the following materials:thermoplastic elastomer, thermoset elastomer, synthetic rubber,thermoplastic vulcanizate, copolymeric ionomer, terpolymeric ionomer,polycarbonate, polyolefin, polyamide, copolymeric polyamide, polyesters,polyester-amides, polyether-amides, polyvinyl alcohols,acrylonitrile-butadiene-styrene copolymers, polyarylate, polyacrylate,polyphenylene ether, impact-modified polyphenylene ether, high impactpolystyrene, diallyl phthalate polymer, metallocene-catalyzed polymers,styrene-acrylonitrile (SAN), olefin-modified SAN,acrylonitrile-styrene-acrylonitrile, styrene-maleic anhydride (S/MA)polymer, styrenic copolymer, functionalized styrenic copolymer,functionalized styrenic terpolymer, styrenic terpolymer, cellulosepolymer, liquid crystal polymer (LCP), ethylene-propylene-diene rubber(EPDM), ethylene-vinyl acetate copolymer (EVA), ethylene propylenerubber (EPR), ethylene vinyl acetate, polyurea, and polysiloxane.Suitable polyamides for use as an additional material in compositionsdisclosed herein also include resins obtained by: (1) polycondensationof (a) a dicarboxylic acid, such as oxalic acid, adipic acid, sebacicacid, terephthalic acid, isophthalic acid or 1,4-cyclohexanedicarboxylicacid, with (b) a diamine, such as ethylenediamine,tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, ordecamethylenediamine, 1,4-cyclohexyldiamine or m-xylylenediamine; (2) aring-opening polymerization of cyclic lactam, such as ε-caprolactam orco-laurolactam; (3) polycondensation of an aminocarboxylic acid, such as6-aminocaproic acid, 9-aminononanoic acid, 11-aminoundecanoic acid or12-aminododecanoic acid; or (4) copolymerzation of a cyclic lactam witha dicarboxylic acid and a diamine. Specific examples of suitablepolyamides include Nylon 6, Nylon 66, Nylon 610, Nylon 11, Nylon 12,copolymerized Nylon, Nylon MXD6, and Nylon 46.

Other preferred materials suitable for use as an additional material ingolf ball compositions disclosed herein include Skypel polyesterelastomers, commercially available from SK Chemicals of South Korea;Septon® diblock and triblock copolymers, commercially available fromKuraray Corporation of Kurashiki, Japan; and Kraton® diblock andtriblock copolymers, commercially available from Kraton Polymers LLC ofHouston, Tex.

Ionomers are also well suited for blending with compositions disclosedherein. Suitable ionomeric polymers include α-olefin/unsaturatedcarboxylic acid copolymer- or terpolymer-type ionomeric resins.Copolymeric ionomers are obtained by neutralizing at least a portion ofthe carboxylic groups in a copolymer of an α-olefin and anα,β-unsaturated carboxylic acid having from 3 to 8 carbon atoms, with ametal ion. Terpolymeric ionomers are obtained by neutralizing at least aportion of the carboxylic groups in a terpolymer of an α-olefin, anα,β-unsaturated carboxylic acid having from 3 to 8 carbon atoms, and anα,β-unsaturated carboxylate having from 2 to 22 carbon atoms, with ametal ion. Examples of suitable α-olefins for copolymeric andterpolymeric ionomers include ethylene, propylene, 1-butene, and1-hexene. Examples of suitable unsaturated carboxylic acids forcopolymeric and terpolymeric ionomers include acrylic, methacrylic,ethacrylic, α-chloroacrylic, crotonic, maleic, fumaric, and itaconicacid. Copolymeric and terpolymeric ionomers include ionomers havingvaried acid contents and degrees of acid neutralization, neutralized bymonovalent or bivalent cations as disclosed herein. Examples ofcommercially available ionomers suitable for blending with compositionsdisclosed herein include Surlyn® ionomer resins, commercially availablefrom E. I. du Pont de Nemours and Company, and Iotek® ionomers,commercially available from ExxonMobil Chemical Company.

Silicone materials are also well suited for blending with compositionsdisclosed herein. Suitable silicone materials include monomers,oligomers, prepolymers, and polymers, with or without adding reinforcingfiller. One type of silicone material that is suitable can incorporateat least 1 alkenyl group having at least 2 carbon atoms in theirmolecules. Examples of these alkenyl groups include, but are not limitedto, vinyl, allyl, butenyl, pentenyl, hexenyl, and decenyl. The alkenylfunctionality can be located at any location of the silicone structure,including one or both terminals of the structure. The remaining (i.e.,non-alkenyl) silicon-bonded organic groups in this component areindependently selected from hydrocarbon or halogenated hydrocarbongroups that contain no aliphatic unsaturation. Non-limiting examples ofthese include: alkyl groups, such as methyl, ethyl, propyl, butyl,pentyl, and hexyl; cycloalkyl groups, such as cyclohexyl andcycloheptyl; aryl groups, such as phenyl, tolyl, and xylyl; aralkylgroups, such as benzyl and phenethyl; and halogenated alkyl groups, suchas 3,3,3-trifluoropropyl and chloromethyl. Another type of suitablesilicone material is one having hydrocarbon groups that lack aliphaticunsaturation. Specific examples include: trimethylsiloxy-endblockeddimethylsiloxane-methylhexenylsiloxane copolymers;dimethylhexenylsiloxyendblocked dimethylsiloxane-methylhexenylsiloxanecopolymers; trimethylsiloxy-endblockeddimethylsiloxane-methylvinylsiloxane copolymers;trimethylsiloxyl-endblockedmethylphenylsiloxane-dimethylsiloxane-methylvinysiloxane copolymers;dimethylvinylsiloxy-endblocked dimethylpolysiloxanes;dimethylvinylsiloxy-endblocked dimethylsiloxane-methylvinylsiloxanecopolymers; dimethylvinylsiloxy-endblocked methylphenylpolysiloxanes;dimethylvinylsiloxy-endblockedmethylphenylsiloxane-dimethylsiloxane-methylvinylsiloxane copolymers;and the copolymers listed above wherein at least one group isdimethylhydroxysiloxy. Examples of commercially available siliconessuitable for blending with compositions disclosed herein includeSilastic® silicone rubber, commercially available from Dow CorningCorporation of Midland, Mich.; Blensil® silicone rubber, commerciallyavailable from General Electric Company of Waterford, N.Y.; andElastosil® silicones, commercially available from Wacker Chemie AG ofGermany.

Other types of copolymers can also be added to the golf ballcompositions disclosed herein. For example, suitable copolymerscomprising epoxy monomers include styrene-butadiene-styrene blockcopolymers in which the polybutadiene block contains an epoxy group, andstyrene-isoprene-styrene block copolymers in which the polyisopreneblock contains epoxy. Examples of commercially available epoxyfunctionalized copolymers include ESBS A1005, ESBS A1010, ESBS A1020,ESBS AT018, and ESBS AT019 epoxidized styrene-butadiene-styrene blockcopolymers, commercially available from Daicel Chemical Industries, Ltd.of Japan.

Compositions disclosed herein can be either foamed or filled withdensity adjusting materials to provide desirable golf ball performancecharacteristics.

PROPHETIC EXAMPLE

It should be understood that the examples below are for illustrativepurposes only. In no manner is the present invention limited to thespecific disclosures herein.

In the following example, two comparative compositions (C1 and C2) and acomposition of the present invention (Example 1) are prepared by mixingthe components in a Brabender mixer for 5-10 minutes. The type andrelative amount of each component to be used is indicated in Table 3.

The resulting rubber compositions are then cured in a compressionmolding press at 350° F. for 11 minutes to obtain spheres, which aresubsequently ground to a diameter of 1.530 inches.

Each of the resulting spheres is evaluated for hardness at the centerand at various distances from the center. Expected results for hardnessare reported in Table 3.

TABLE 3 C1 C2 Example 1 Composition SE BR-1220¹ 100 100 100 (parts byweight) SR526² 29 30 40 (parts by weight) Perkadox ® BC³ 0 1 1.25 (partsby weight) Trigonox ® 265³ 0.53 0 0 (parts by weight) zinc oxide 5 5 5(parts by weight) zinc pentachlorothiophenol 0 0.5 0.5 (parts by weight)hydroquinone 0 0 0.75 (parts by weight) filler * * * Hardness surfacehardness (Shore C) 76 84 92 center hardness (Shore C) 65 63 58 hardnessgradient 11 21 34 ¹SE BR-1220 is a high cis-1,4 polybutadienecommercially available from The Dow Chemical Company. ²SR526 is a zincdiacrylate coagent commercially available from Sartomer Industries, Inc.³Perkadox ® BC and Trigonox ® 265 are peroxide free radical initiatorscommercially available from Akzo Nobel. *The amount of filler used canbe adjusted to hit target specific gravity.

When numerical lower limits and numerical upper limits are set forthherein, it is contemplated that any combination of these values may beused.

All patents, publications, test procedures, and other references citedherein, including priority documents, are fully incorporated byreference to the extent such disclosure is not inconsistent with thisinvention and for all jurisdictions in which such incorporation ispermitted.

While the illustrative embodiments of the invention have been describedwith particularity, it will be understood that various othermodifications will be apparent to and can be readily made by those ofordinary skill in the art without departing from the spirit and scope ofthe invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the examples and descriptions setforth herein, but rather that the claims be construed as encompassingall of the features of patentable novelty which reside in the presentinvention, including all features which would be treated as equivalentsthereof by those of ordinary skill in the art to which the inventionpertains.

1. A golf ball consisting of: a solid, single-layer core formed from arubber composition, the rubber composition comprising: (a) a baserubber; (b) at least 0.05 parts by weight of a free radical initiatorper 100 parts of the base rubber; and (c) at least 0.1 parts by weightof a hydroquinone per 100 parts of the base rubber; wherein a ratio(P_(HQ)/P_(FRI)) of the amount of the hydroquinone present in the rubbercomposition (P_(HQ)), measured in parts by weight per 100 parts of thebase rubber, to the amount of free radical initiator present in therubber composition (P_(FRI)), measured in parts by weight per 100 partsof the base rubber, is from 0.05 to 2; and a cover; wherein the core hasa center Shore C hardness (H_(CENTER)) and a surface Shore C hardness(H_(SURFACE)), and H_(SURFACE)−H_(CENTER)≧25 Shore C units.
 2. The golfball of claim 1, wherein H_(SUFACE)−H_(CENTER)≧30 Shore C units.
 3. Thegolf ball of claim 1, wherein H_(SURFACE)−H_(CENTER)≧35 Shore C units.4. The golf ball of claim 1, wherein H_(SURFACE)−H_(CENTER)≧40 Shore Cunits.
 5. The golf ball of claim 1, wherein H_(SURFACE)−H_(CENTER)≧45Shore C units.
 6. The golf ball of claim 1, wherein the amount of thehydroquinone present in the rubber composition is at least 0.2 parts byweight per 100 parts of the base rubber.
 7. The golf ball of claim 1,wherein P_(HQ)/P_(FRI) is from 0.25 to 0.45.
 8. The golf ball of claim1, wherein the hydroquinone is selected from hydroquinone,tetrachlorohydroquinone, and 2-(2-chlorophenyl)hydroquinone hydrate. 9.The golf ball of claim 1, wherein the rubber composition issubstantially free of organosulfur compounds.
 10. A golf ball consistingof: a solid, single-layer core having a diameter of from 1.51 inches to1.59 inches and formed from a rubber composition, the rubber compositioncomprising: (a) a base rubber; (b) at least 0.05 parts by weight of afree radical initiator per 100 parts of the base rubber; and (c) atleast 0.1 parts by weight of a hydroquinone per 100 parts of the baserubber; wherein a ratio (P_(HQ)/P_(FRI)) of the amount of thehydroquinone present in the rubber composition (P_(HQ)), measured inparts by weight per 100 parts of the base rubber, to the amount of freeradical initiator present in the rubber composition (P_(FRI)), measuredin parts by weight per 100 parts of the base rubber, is from 0.05 to 2;and a cover.
 11. The golf ball of claim 10, wherein the core has acenter hardness (H_(CENTER)) of 80 Shore C or less and a surfacehardness (H_(SURFACE)) of greater than 80 Shore C, and whereinH_(SURFACE)−H_(CENTER)≧25 Shore C units.
 12. The golf ball of claim 10,wherein H_(SURFACE)−H_(CENTER)≧30 Shore C units.
 13. The golf ball ofclaim 10, wherein H_(SURFACE)−H_(CENTER)≧40 Shore C units.
 14. The golfball of claim 10, wherein H_(SURFACE)−H_(CENTER)≧45 Shore C units. 15.The golf ball of claim 10, wherein P_(HQ)/P_(FRI) is from 0.25 to 0.45.16. The golf ball of claim 10, wherein the hydroquinone is selected fromhydroquinone, tetrachlorohydroquinone, and2-(2-chlorophenyl)hydroquinone hydrate.
 17. The golf ball of claim 10,wherein the rubber composition is substantially free of organosulfurcompounds.